This invention relates to a fuel supply system for an internal combustion engine, and the invention is especially adapted for use with two-cycle engines having a plurality of reed valves, particularly where those valves are associated with a V-shaped reed valve cage. In arrangements of this type, various factors tend to cause irregularities in the flow of the fuel/air mixture. Thus, the flow tends to increase in the central region of the flow passage and tends to decrease adjacent to the boundaries of the passage. Moreover, in arrangements of this type, and especially where a V-shaped valve cage is used, the cross-sectional area of the fuel/air flow passage in regions upstream of the reed valves varies at different distances upstream of the valve cage and also in the immediate vicinity of the reed valves themselves mounted on the V-shaped reed valve cage.
Because of these variations in the flow and for reasons explained more fully hereinafter, it is desirable to introduce into the flow path at least one element configured and positioned to divert the flow in different regions of the flow path, the dimension of the flow providing for reduction in the variations which tend to occur.
Because of tendency for the flow to become concentrated in the central region of the flow path, it is desirable to position a flow diverting element in the central region of the flow path, the element being shaped and positioned to divert or direct the flow away from the central region and toward the boundary walls of the flow path.
Also, because of the differences in cross-sectional dimension of the flow passage in various regions of the intake duct, the velocity of flow of the fuel/air mixture changes in different regions of the flow passage, the flow velocity being relatively low in regions of relatively large cross-sectional flow area and being relatively high in regions of relatively small cross-sectional flow area. Fluctuations in velocity are accompanied by energy loss because of changes in the dynamic inertia of the fuel/air mixture travelling through the intake duct. In turn, this results in a lower overall average velocity, with consequent reduction in the overall quantity of the fuel/air mixture being delivered through the system and into the engine.
According to the present invention, this irregularity in velocity of flow may be reduced by employing a flow diverting element adapted to reduce the irregularity in velocity of flow.
My prior U.S. Pat. No. 4,228,770 discloses the use of a bar or element of aeroform shape in a flow passage upstream of the reed valves, the bar being positioned to reduce variation in cross-sectional flow area and the resultant fluctuations in flow velocity and thus in the dynamic or kinetic energy losses. The arrangements of the present application also accomplish this general purpose; but in addition, the arrangements of the present invention contemplate the use of a flow diverting element differently positioned and of different configuration as compared with the element disclosed in my prior patent. Thus, whereas in my prior patent the aeroform element is comprised of a bar of varying contour in only one plane, the element used in accordance with the present invention is of varying contour in two planes, preferably at right angles to each other.
In several embodiments of the elements disclosed in the present application, the element or elements of varying contour are of aeroform shape in either one or both of the two planes referred to above.
Still further, the arrangement of the present invention provides for positioning of the element so that the element diverts the flow from the central region toward the boundaries and especially toward the boundaries which are most remote from the central region. For example, the diverting element is desirably closely nested within the central region of the V-shaped reed valve cage commonly employed in association with the reed valves for the engine. Moreover, the present invention provides for the employment of an element of aeroform shape in which the aeroform contour is present not only in a plane containing the flow axis and the apex of the reed valve cage, as is the case in my prior patent, but also in a plane containing the flow axis and at right angles to the apex of the reed valve cage. Still further, the improved aeroform element employed in accordance with the present invention has an edge thereof lying in said plane perpendicular to the reed cage apex and proportioned so that that edge may be mounted within the V-shaped reed cage with the extremity of the edge portion lying closely adjacent to the interior wall of the reed cage. In this way, with reed cages having a plurality of laterally spaced valve ports, the edge of the aeroform element, when closely nested within the reed cage, effectively divides the interior of the reed cage into two portions respectively communicating with the valve ports lying at opposite sides of the aeroform element.
In accordance with another aspect of the invention, the element introduced into the flow channel is proportioned, configured and mounted in a manner which increases the volume of the element in the central region of the flow passage, and at the same time, decreases the volume of the element in the marginal regions adjoining the boundaries of the flow passage. By this arrangement, the flow is distributed more uniformly throughout the entire cross-sectional flow area of the flow passage. This is of particular importance in installations in which the overall cross-sectional flow area, for instance, in the region of the entrance into the V-shaped valve cage, is of generally rectangular shape with the dimension paralleling the axis of the reed cage apex considerably greater than the transverse dimension. Indeed, in reed cages having three or four valve ports at each side of the reed cage, the dimension paralleling the axis of the reed cage apex may even be as much as two times the dimension in the transverse direction. Without provision for increasing the uniformity of the fuel/air mixture, the tendency for the flow to concentrate in the central region results in reduction of flow through the outboard valve ports to such an extent as to impair the overall input of the fuel/air mixture, with consequent impairment of the engine power output, and this detrimental effect is present at any engine speed.
Having the foregoing in mind, the arrangements of the present invention, in contrast to the arrangement of my prior U.S. Pat. No. 4,228,770, provide for mounting devices, such as the mounting posts for the element introduced into the flow path of the intake passage, which mounting posts are not located in the regions most remotely spaced from the central zone of the flow passage, as in the prior patent above referred to, but which are located at the boundaries of the flow passage which are closest to the central flow region. By locating the mounting posts as just mentioned, increased flow is provided, particularly adjacent those boundaries of the flow passage which are most remote from the central region. This is of great importance, even if the element introduced into the flow passage is not proportioned to result in substantial equalization of the overall cross-sectional flow area in various zones upstream and downstream of the flow passage. Furthermore, this feature is desirably employed even if the element introduced into the flow passage is not of aeroform contour; but for various reasons, the aerofrom contour elements are, of course preferred because of the fact that the aeroform shape tends to minimize localized eddy currents which also tend to decrease the overall efficiency of feed of the fuel/air mixture.
Having the above in mind, the element mounted in the flow path in accordance with the present invention is preferably provided with mounting posts lying in a plane at right angles to the reed cage apex; and at opposite sides of that plane, the end portions of the element are terminated short of the reed cage end walls, thereby minimizing obstruction of the flow passage in the region toward the ends of the reed cage.
The foregoing and various other features of the invention provide extensive increase in fuel flow capacity, particularly because of the striking increase in uniformity of flow velocity and flow distribution. As a result, actual tests have shown that the arrangement of the invention greatly increases the fuel/air input capacity of the system, particularly at high engine speeds where maximum input of fuel/air is desired.